Photolithography method and photolithography system

ABSTRACT

A photolithography method includes dispensing a first liquid onto a first target layer formed over a first wafer through a nozzle at a first distance from the first target layer; capturing an image of the first liquid on the first target layer; patterning the first target layer after capturing the image of the first liquid; comparing the captured image of the first liquid to a first reference image to generate a first comparison result; responsive to the first comparison result, positioning the nozzle and a second wafer such that the nozzle is at a second distance from a second target layer on the second wafer; dispensing a second liquid onto the second target layer formed over the second wafer through the nozzle at the second distance from the second target layer; and patterning the second target layer after dispensing the second liquid.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. Non-Provisional patentapplication Ser. No. 16/889,465, filed Jun. 1, 2020 and entitled“Photolithography Method and Photolithography System,” which is adivisional of U.S. Non-Provisional patent application Ser. No.16/225,776, filed Dec. 19, 2018 and entitled “Photolithography Methodand Photolithography System,” now U.S. Pat. No. 10,670,540, which claimspriority to U.S. Provisional Patent Application Ser. No. 62/692,393,filed Jun. 29, 2018 and entitled “Chemical Dispensing System forSemiconductor Fabrication,” the entire disclosure of which isincorporated herein by reference.

BACKGROUND

Semiconductor devices are used in a variety of electronic applications,such as personal computers, cell phones, digital cameras, and otherelectronic equipment. Semiconductor devices are typically fabricated bysequentially depositing insulating or dielectric layers, conductivelayers, and semiconductor layers of materials over a semiconductorsubstrate, and patterning the various material layers using lithographyto form circuit components and elements thereon.

The semiconductor industry continues to improve the integration densityof various electronic components (e.g., transistors, diodes, resistors,capacitors, etc.) by continual reductions in minimum feature size, whichallows more components to be integrated into a given area. These smallerelectronic components also require smaller packages that utilize lessarea than the packages of the past, in some applications.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1A-1C illustrate a block diagram of a method of forming somesemiconductor devices in accordance with some embodiments.

FIGS. 2A-2L illustrate cross sectional views of a first wafer at variousstages of fabrication in accordance with some embodiments of the presentdisclosure.

FIGS. 3A-3C illustrate schematic diagrams of a wafer processing systemfor a method of coating bottom, middle, and top layers of a tri-layerresist respectively on the first wafer in accordance with someembodiments of the present disclosure.

FIGS. 3D and 3E illustrate schematic diagrams of another waferprocessing system for methods of developing and rinsing the first waferrespectively in accordance with some embodiments of the presentdisclosure.

FIGS. 4A-4D are block diagrams of some wafer processing systems inaccordance with some embodiments of the present disclosure.

FIGS. 5A-5E illustrate captured images of the first wafer that coatsbottom, middle, and top layers of the tri-layer resist and that developsand rinses the tri-layer thereof in accordance with some embodiments ofthe present disclosure.

FIGS. 6A-6E illustrate reference images of the first wafer that coatsbottom, middle, and top layers of the tri-layer resist and that developsand rinses the tri-layer thereof in accordance with some embodiments ofthe present disclosure.

FIGS. 7A-7L illustrate cross sectional views of a second wafer atvarious stages of fabrication in accordance with some embodiments of thepresent disclosure.

FIGS. 8A-8C illustrate schematic diagrams of the wafer processing systemfor a method of coating bottom, middle, and top layers of a tri-layerresist respectively on the second wafer in accordance with someembodiments of the present disclosure.

FIGS. 8D and 8E illustrate schematic diagrams of the other waferprocessing system for methods of developing and rinsing the second waferrespectively in accordance with some embodiments of the presentdisclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

The present disclosure in various embodiments is generally related tomethods for semiconductor device fabrication, and more particularly tomethods of lithography patterning. In lithography patterning, a resistfilm is formed on a substrate and further exposed to develop in adeveloper. The developer removes portions of the resist film, therebyforming a resist pattern which may include line patterns and/or trenchpatterns. The resist pattern may undergo additional rinsing andtreatment processes to be further solidified. The resist pattern is usedas an etch mask in subsequent etching processes, transferring thepattern to underlying layers.

FIGS. 1A-1C illustrate an exemplary method M for fabrication of asemiconductor device in accordance with some embodiments. The method Mincludes a relevant part of the entire manufacturing process. The methodM may be implemented, in whole or in part, by a system employing deepultraviolet (DUV) lithography, extreme ultraviolet (EUV) lithography,electron beam (e-beam) lithography, x-ray lithography, and otherappropriate lithography processes to improve pattern dimension accuracy.Additional operations can be provided before, during, and after themethod M, and some operations described can be replaced, eliminated,modified, moved around, or relocated for additional embodiments of themethod. One of ordinary skill in the art may recognize other examples ofsemiconductor fabrication processes that may benefit from aspects of thepresent disclosure. The method M is an example, and is not intended tolimit the present disclosure beyond what is explicitly recited in theclaims.

The method M is described below in conjunction with FIGS. 2A-2L in whicha semiconductor device 200 is fabricated by using the method M. FIGS.2A-2L illustrate the semiconductor device 200 at various stages of themethod M according to some embodiments of the present disclosure. Themethod M begins at block S101 where a first target layer is formed overa first wafer. Referring to FIG. 2A, in some embodiments of block S101,the first wafer W1 includes one or more layers of material orcomposition. In some embodiments, the first wafer W1 is a semiconductorsubstrate. In another embodiment, the first wafer W1 includes silicon ina crystalline structure. In alternative embodiments, the first wafer W1includes other elementary semiconductors such as germanium; a compoundsemiconductor such as silicon carbide, gallium arsenide, indiumarsenide, and indium phosphide; an alloy semiconductor such as GaAsP,AlInAs, AlGaAs, InGaAs, GaInP, and/or GaInAsP; or combinations thereof.The first wafer W1 may include a silicon on insulator (SOI) substrate,be strained/stressed for performance enhancement, include epitaxialregions, include isolation regions, include doped regions, include oneor more semiconductor devices or portions thereof, include conductiveand/or non-conductive layers, and/or include other suitable features andlayers.

Alternatively or additionally, the first wafer W1 may include otherelementary semiconductor materials such as germanium (Ge). In someembodiments, the first wafer W1 is made of a compound semiconductor suchas silicon carbide (SiC), gallium arsenic (GaAs), indium arsenide(InAs), or indium phosphide (InP). In some embodiments, the first waferW1 is made of an alloy semiconductor such as silicon germanium (SiGe),silicon germanium carbide (SiGeC), gallium arsenic phosphide (GaAsP), orgallium indium phosphide (GaInP). In some embodiments, the first waferW1 includes an epitaxial layer. For example, the first wafer W1 has anepitaxial layer overlying a bulk semiconductor. In some otherembodiments, the first wafer W1 may be a germanium-on-insulator (GOI)substrate.

In some embodiments, the first wafer W1 may have various deviceelements. Examples of device elements that are formed in the first waferW1 include transistors (e.g., metal oxide semiconductor field effecttransistors (MOSFET), complementary metal oxide semiconductor (CMOS)transistors, bipolar junction transistors (BJT), high-voltagetransistors, high-frequency transistors, p-channel and/or n-channelfield-effect transistors (PFETs/NFETs), etc.), diodes, and/or otherapplicable elements. Various processes are performed to form the deviceelements, such as deposition, etching, implantation, photolithography,annealing, and/or other suitable processes.

As shown in FIG. 2A, a target layer 204 is formed on the first wafer W1.In some embodiments, the target layer 204 is a hard mask layer includingmaterial(s) such as amorphous silicon (a-Si), silicon oxide, siliconnitride (SiN), titanium nitride, or other suitable material orcomposition. In some embodiments, the target layer 204 includes ananti-reflection coating (ARC) layer such as a nitrogen-freeanti-reflection coating (NFARC) layer including material(s) such assilicon oxide, silicon oxygen carbide, or plasma enhanced chemical vapordeposited silicon oxide.

Returning to FIG. 1A, the method M then proceeds to block S102 where thefirst target layer is coated with a first bottom layer of a firstmulti-layer resist using a first nozzle at a first distance from thefirst target layer, and an image of the first bottom layer is capturedduring the coating. In some embodiments of block S102, as illustrated inFIG. 2B, a bottom layer 212 of a first multi-layer resist (e.g., atri-layer resist 210 shown in FIG. 2F) is formed over the target layer204.

With reference to FIG. 3A, the bottom layer 212 is coated on the targetlayer 204 using a spin-on coating method. Specifically, in the spin-oncoating process, a liquid material of the bottom layer 212 is dispensedon a substantial center region of first wafer W1 in the catch cup 31 bythe dispensing nozzle 331 (see FIG. 3A), and the wafer stage 32 (seeFIG. 3A) simultaneously rotates the first wafer W1 at a rotationalspeed. In some embodiments, the dispensing nozzle 331 scans across thesurface of the first wafer W1 during the coating. As shown in FIG. 3A,the dispensing nozzle 331 is separated from the target layer 204 by adistance D1. For example, the distance D1 is from about 0.8 mm to about1.2 mm, but the present disclosure is not limited thereto.

In some embodiments, the bottom layer 212 includes a polar componentsuch as a polymer with hydroxyl or phenol groups that can attract orbond with amines or nitrogen containing compounds that might diffuse outof the underlying dielectric materials. In some embodiments, the bottomlayer 212 includes an i-line photoresist that normally includes aNovolac resin that is prepared by reacting a cresol, xylenol, or othersubstituted phenols with formaldehyde. The i-line photoresist may beparticularly useful in preventing amines such as ammonia from reachingan overlying photoresist that is exposed to produce a pattern.Alternatively, the bottom layer 212 may be a deep UV photoresist thattypically includes polymers having hydroxystyrene groups the bottomlayer 212 may be formed from either a positive tone or negative tonephotoresist.

FIG. 3A is a wafer processing system 3 for coating a first liquid film(such as the bottom layer 212 in the tri-layer resist 210 shown in FIG.2B) on the first wafer W1 in accordance with some embodiments of thepresent disclosure. FIG. 4A is a block diagram of the wafer processingsystem 3 in accordance with some embodiments of the present disclosure.The wafer processing system 3 includes a processing chamber 30, atransferring module (not shown), a liquid dispensing module 40, anin-line monitoring module 50 (shown in FIG. 4A and may also be referredto as in-sequence monitoring module or a color imaging system), and acontroller 60 (shown in FIG. 4A).

As shown in FIG. 3A, the processing chamber has an interior space 300defined by a number of walls, such as a lateral wall 301, a bottom wall302, and a top wall 303. The lateral wall 301 is connected to edges ofthe bottom wall 302 and extends away from the bottom wall 302. The topwall 303 is connected to the distal end of the lateral wall 301. In someembodiments, the interior space 300 is secluded from the ambientenvironment. The interior space 300 communicates to the ambientenvironment via a slot 305 formed on the lateral wall 301. The slot 305allows the transferring module to pass through. The processing chamber30 further includes a catch cup 31, a wafer stage 32, and an edge beadrinse (EBR) nozzle 33, in accordance with some embodiments. The catchcup 31, the wafer stage 32, and the EBR nozzle 33 are positioned in theinterior space 300.

In some embodiments, the catch cup 31 is configured to provide anenvironment for coating a layer (e.g., the bottom layer 212) on thefirst wafer W1 and developing an exposed layer (e.g., the bottom layer212 after exposure) on the first wafer W1. The catch cup 31 is acircular cup having an open top 314. The upper portion 313 of the cupwall 312 tilts inward to facilitate retaining waste photoresist withinthe catch cup 31. The catch cup 31 is connected to an exhaust system viaa liquid waste drain 34 formed on the bottom wall 302. As a result, thecatch cup 31 is able to catch and drain waste liquid solution in aliquid film spin-on coating process via the liquid waste drain 34.

In some embodiments, the wafer stage 32 is disposed in the catch cup 31.In some embodiments, the wafer stage 32 is configured for holding,positioning, moving, and otherwise manipulating the first wafer W1. Insome embodiments, the wafer stage 32 is arranged to rotate about a mainaxis C1. The first wafer W1 may be secured on the wafer stage 32 by aclamping mechanism, such as vacuum clamping or e-chuck clamping. Thewafer stage 32 is designed and configured to be operable fortranslational and rotational motions. In some embodiments, the waferstage 32 is further designed to tilt or dynamically change the tiltangle. In some embodiments, the wafer stage 32 is fitted with a suitableheating mechanism to heat the first wafer W1 to a desired temperature.

In some embodiments, the EBR nozzle 33 is disposed in the catch cup 31.The EBR nozzle 33 is used to supply a liquid solution over the firstwafer W1, when the first wafer W1 is disposed in the catch cup 31. TheEBR nozzle 33 is connected to a source unit (not shown) to receive thechemical solution from the source unit.

In FIG. 3A, the liquid dispensing module 40 includes one or more drivingelement 45 (shown in FIG. 4A), a first drive mechanism 41, a seconddrive mechanism 42, a dispensing nozzle 331, and a distance sensor 55,in accordance with some embodiments. The driving element 45 shown inFIG. 4A, such as a motor, is controlled by the controller 60 and iscoupled to the first drive mechanism 41 and the second drive mechanism42. The driving element 45 shown in FIG. 4A is used to actuate the firstdrive mechanism 41 to move in a vertical direction Y (as shown in FIG.3A). In some embodiments, the first drive mechanism 41 is rotatableabout a vertical axis as well. In some embodiments, the driving element45 is a programmable controller or the like.

In some embodiments, the dispensing nozzle 331 is mounted at the seconddrive mechanism 42. The dispensing nozzle 331 is used to dispense aliquid to the first wafer W1. The dispensing nozzle 331 is connected toa liquid source (not shown in figures) to receive the liquid.

In FIGS. 3A and 4A, the in-line monitoring module 50 includes an imagesensor 52, an image processor 53, and a reference image database 54, inaccordance with some embodiments. The image sensor 52 is located at theinterior space 300 of the processing chamber 30. In some embodiments,the image sensor 52 has a field of view (FOV) covering the wafer stage32, so that the image sensor 52 can capture an image of a wafer (e.g.,the wafers W1 and W2) held by the wafer stage 32. In some embodiments,the image sensor 52 is mounted at the catch cup 31.

In some embodiments, the image sensor 52 includes a charge-coupleddevice (CCD). The CCD is a highly sensitive photon detector. The CCD isdivided into a large number of small, light-sensitive areas (known assensing pixels) which can be used to build up an image of the scene ofinterest. A photon of light that falls within the area defined by one ofthe sensing pixels will be converted into one (or more) electrons, andthe number of electrons collected will be directly proportional to theintensity of the scene at each sensing pixel. When the CCD is clockedout, the number of electrons in each sensing pixel is measured and thescene can be reconstructed.

In FIGS. 3A and 4A, the image processor 53 is connected to the imagesensor 52 to receive the captured image from the image sensor 52 duringthe spin-on coating process. Then, the image processor 53 compares theimage captured by the image sensor 52 to a reference image 540 stored ina reference image database 54 and thus produce a comparison resultshowing the differences between the two. The comparison result can beused to determine a height of the dispensing nozzle 331 for processingof the next wafer, such as a second wafer W2 which will be discussed ingreater detail below with respect to FIGS. 7A-8E. The second wafer W2may be processed in the processing chamber 30 after the processing ofthe first wafer W1.

In some embodiments, the controller 60 sends a control signal to thedriving element 45 of the liquid dispensing module 40 to actuate thefirst drive mechanism 41 moving in the vertical direction Y (as shown inFIG. 3A). Accordingly, the dispensing nozzle 331 mounted at the seconddrive mechanism 42 is able to move relatively to the first wafer W1 inthe vertical direction Y. In some embodiments, the controller 60 caninclude a central processing unit (CPU), a memory, and support circuits,e.g., input/output circuitry, power supplies, clock circuits, cache, andthe like. The memory is connected to the CPU. The memory is anon-transitory computable readable medium, and can be one or morereadily available memory such as random access memory (RAM), read onlymemory (ROM), floppy disk, hard disk, or other form of digital storage.In addition, although illustrated as a single computer, the controller60 can be a distributed system, e.g., including multiple independentlyoperating processors and memories.

In some embodiments of dispensing a liquid material of bottom layer 212,referring now to FIG. 5A, the image sensor 52 captures an image 212 c ofthe bottom layer 212 during the dispensing. Specifically, the capturedimage 212 c shows a rippled and corrugated bottom layer 212 because thedispensed material of bottom layer 212 is liquid. For example, thecaptured image 212 c of the bottom layer 212 has a pitch P1 and/or anarc feature A1 at a position S1 over the first wafer W1. The imageprocessor 53 shown in FIG. 4A receives the captured image 212 c from theimage sensor 52 during the spin-on coating process (i.e., duringdispensing material of the bottom layer 212). Then, the image processor53 compares the captured image 212 c of the bottom layer 212 to acorresponding reference image 540 (e.g., a reference image 212 r of adesirable bottom layer as shown in FIG. 6A), and then sends thecomparison result to the controller 60 for the processing of the nextwafer, such as a second wafer W2 which will be discussed in greaterdetail below with respect to FIGS. 7A-8E.

Returning to FIG. 1A, the method M then proceeds to block S103 where thefirst bottom layer is pre-baked. With reference to FIG. 2C, in someembodiments of block S103, a pre-baking process 220 may be performed atan elevated temperature to evaporate the solvent in the bottom layer 212for a time duration sufficient to cure and dry the bottom layer 212.

Returning to FIG. 1A, the method M then proceeds to block S104 where thefirst nozzle is vertically moved. With reference to FIG. 3B, in someembodiments of block S104, before coating a next layer onto the firstwafer W1, the first drive mechanism 41 may lift the dispensing nozzle331 to a predetermined height, such that the dispensing nozzle 331 willbe separated from the target layer 204 by a distance D2 which is greaterthan the distance D1 shown in FIG. 3A. The difference between distancesD1 and D2 is associated with a difference between the viscosities of thebottom layer 212 and a middle layer 214 which will be subsequentlyformed on the bottom layer 212. For example, the distance D2 is fromabout 1.2 mm to about 1.8 mm, but the present disclosure is not limitedthereto. In some embodiment, the viscosity of the middle layer 214 maybe higher than that of the bottom layer 212. In this way, the middlelayer 214 coated using the dispensing nozzle 331 at the distance D2 willhave a better profile (e.g., better flatness) compared to that at thedistance D1.

Details of vertically moving the dispensing nozzle 331 can be referredto FIGS. 3B and 4B. FIG. 3B is a wafer processing system 3 in accordancewith some embodiments of the present disclosure. FIG. 4B is a blockdiagram of the wafer processing system 3 in accordance with someembodiments of the present disclosure.

As shown in FIG. 3B, the distance sensor 55 is mounted at a distal endof the second drive mechanism 42 to detect a distance between thedispensing nozzle 331 and the first wafer W1. The distance sensor 55 maybe a real time monitor and feedback a height of the dispensing nozzle331. The controller 60 (see FIG. 4B) is connected to the distance sensor55 to periodically retrieve the electronic signal from the distancesensor 55.

The driving element 45, such as a motor, is controlled by the controller60 and is coupled to the first drive mechanism 41. Specifically, thecontroller 60 is configured to send a control signal to the drivingelement 45 of the liquid dispensing module 40 to actuate the first drivemechanism 41 moving in the vertical direction Y (as shown in FIG. 3B).In some embodiments, the control signal from the controller 60 isassociated with a measured distance from the distance sensor 55. Forexample, if the measured distance is less than the predetermineddistance D2 which is associated with dispensing a material of the middlelayer 214, the controller 60 can provide a control signal to trigger thedriving element 45 to upwardly move the dispensing nozzle 331.

When the distance between the dispensing nozzle 331 and the target layer204 is substantially equal to the distance D2, the controller 60 willsend a control signal to the driving element 45 to stop (or halt) theoperation of the driving element 45. Accordingly, the dispensing nozzle331 and the target layer 204 will maintain the distance D2 therebetweenin the vertical direction Y.

Returning to FIG. 1A, the method M then proceeds to block S105 where thefirst bottom layer is coated with a first middle layer of the firstmulti-layer resist using the first nozzle at a second distance from thefirst target layer, and an image of the first middle layer is capturedduring the coating.

With reference to FIGS. 2D and 3B, in some embodiments of block S105,the middle layer 214 is coated on the bottom layer 212. In detail, asecond liquid film, such as a liquid material of the middle layer 214,is dispensed on the bottom layer 212 through the dispensing nozzle 331separated from the target layer 204 by the distance D2, and the waferstage 32 simultaneously rotates the first wafer W1 at a rotationalspeed. The middle layer 214 includes a material different from that ofthe bottom layer 212. In some embodiments, the middle layer 214 has aviscosity different that of the bottom layer 212.

If the dispensing nozzle 331 is separated from the target layer 204 bythe distance D1 shown in FIG. 3A rather than the distance D2, the middlelayer 214 dispensed through the dispensing nozzle 331 might have anon-uniform thickness (i.e., poor flatness) on the first wafer W1. Forexample, a central portion of the middle layer 214 will be thicker thanother portions of the middle layer 214. However, because the middlelayer 214 is formed using the dispensing nozzle 331 at the distance D2rather than the distance D1, thickness uniformity (i.e., flatness) ofthe resulting middle layer 214 can be improved.

In some other embodiment, the viscosity of the middle layer 214 may belower than that of the bottom layer 212. In such embodiments, in blockS104 of the method M in FIG. 1, the first drive mechanism 41 may lowerthe dispensing nozzle 331, such that the nozzle 331 will be separatedfrom the target layer 204 by the distance D2 less than the distance D1to mitigate liquid splashing during the coating process of middle layer214.

In some embodiments, the process time duration for coating the middlelayer 214 is different from that for coating the bottom layer 212. Thetime duration difference is associated with the difference between theviscosities of the bottom and middle layers 212 and 214. For example,the process time duration for coating the middle layer 214 may be longerthan that for coating the bottom layer 212. In some other embodiments,the process time duration for coating the middle layer 214 may beshorter than that for coating the bottom layer 212. This can be due, atleast in part, because a different viscosity can affect thecorresponding process time duration. Also, the dispense profile can beoptimized by automatically fine-tuning the nozzle height for differentchemical viscosities

In some embodiments, the middle layer 214 functions as ananti-reflective coating (ARC), which prevents the light from reachingthe underlying resist layer during the time when the overlyingphotoresist layer is exposed. Also, the middle layer 214 may be selectedfrom a material that is immiscible with organic solvents used forsubsequently resist coating and/or has optical properties minimizingreflectivity of light during exposure of photoresist. For example, themiddle layer 214 may be a negative organic ARC, a negative dyed resist,or a Deep UV ARC.

In some embodiments of dispensing a liquid material of middle layer 214,referring now to FIG. 5B, the image sensor 52 captures an image 214 c ofthe middle layer 214 during the dispensing. Specifically, the capturedimage 214 c shows a rippled and corrugated middle layer 214 because thedispensed material of bottom layer 212 is liquid. For example, thecaptured image 214 c of the bottom layer 214 has a pitch P2 and/or anarc feature A2 at a position S2 over the first wafer W1. In FIG. 4A, theimage processor 53 is connected to the image sensor 52 to receive thecaptured image 214 c during the coating process (i.e., during dispensingmaterial of the middle layer 214). Then, the image processor 53 comparesthe captured image 214 c of the middle layer 214 to a correspondingreference image 540 (e.g., a reference image 214 r of a desirable middlelayer as shown in FIG. 6B), and then sends the comparison result to thecontroller 60 for the processing of the next wafer, such as a secondwafer W2 which will be discussed in greater detail below with respect toFIGS. 7A-8E.

Returning to FIG. 1A, the method M then proceeds to block S106 where thefirst middle layer is pre-baked. With reference to FIG. 2E, in someembodiments of block S106, the pre-baking process 220 may be performedat an elevated temperature to evaporate the solvent in the middle layer214 for a time duration sufficient to cure and dry the middle layer 214.

Returning to FIG. 1A, the method M then proceeds to block S107 where thefirst nozzle is vertically moved. With reference to FIG. 3C, in someembodiments of block S107, before coating a next layer onto the firstwafer W1, the first drive mechanism 41 may lower the dispensing nozzle331 to a predetermined height, such that the dispensing nozzle 331 willbe separated from the target layer 204 by a distance D3 which isdifferent from the distances D1 and D2 shown in FIGS. 3A and 3B. Thedistance difference is associated with a viscosity difference among thebottom layer 212, the middle layer 214, and a top layer 216 which willbe subsequently formed on the middle layer 214. In some embodiment, theviscosity of the top layer 216 may be less than that of the middle layer214. In some embodiments, the distance D3 is from 0.6 mm to about 0.8mm, but the present disclosure is not limited thereto.

Returning to FIG. 1A, the method M then proceeds to block S108 where thefirst middle layer is coated with a first top layer of the firstmulti-layer resist using the first nozzle at a third distance from thefirst target layer, and an image of the first top layer is capturedduring the coating.

With reference to FIGS. 2F and 3C, in some embodiments of block S105,the top layer 216 is coated on the middle layer 214. In detail, a thirdliquid film, such as a liquid material of the top layer 216, isdispensed on the first wafer W1 through the dispensing nozzle 331separated from the target layer 204 by a distance D3, and the waferstage 32 simultaneously rotates the first wafer W1 at a rotationalspeed. The top layer 216 includes a material different from that of thebottom layer 212 and/or the middle layer 214. In some embodiments, thetop layer 216 has a viscosity different that of the bottom layer 212and/or the middle layer 214.

If the dispensing nozzle 331 is separated from the target layer 204 bythe distance D1 or D2 rather than the distance D3, the top layer 216dispensed through the dispensing nozzle 331 might have aggravated liquidsplashing phenomenon, thus leading to non-uniform thickness (i.e., poorflatness) of the resulting top layer 216. However, because the top layer216 is formed using the dispensing nozzle 331 at the distance D3 ratherthan the distance D1 or D2, thickness uniformity (i.e., flatness) of theresulting top layer 216 can be improved.

In some other embodiment, the viscosity of the top layer 216 may belarger than that of the middle layer 214. In such embodiments, in blockS107 of the method M in FIG. 1, the first drive mechanism 41 may liftthe dispensing nozzle 331 to a predetermined height, such that thenozzle 331 will be separated from the target layer 204 by a distance D3greater than the distances D1 and/or D2 shown in FIG. 3A, so as toimprove thickness uniformity (i.e., flatness) of the resulting top layer216.

In some embodiments, the process time duration for coating the top layer216 is different from that for coating the middle layer 214. The timeduration difference is associated with the difference between theviscosities of the middle and top layers 214 and 216. For example, theprocess time duration for coating the top layer 216 may be shorter thanthat for coating the middle layer 214. In some other embodiments, theprocess time duration for coating the top layer 216 may be longer thanthat for coating the middle layer 214. This can be due, at least inpart, because a different viscosity can affect the corresponding processtime duration. Also, the dispense profile can be optimized byautomatically fine-tuning the nozzle height for different chemicalviscosities.

In some embodiments, the top layer 216 may be a deep UV photoresist. Thephotoresist may be either a positive tone or a negative tone material,which is then exposed and developed in an aqueous base solution to forma pattern which will be transferred to the underlying resist layers fordefining a trench in subsequent processes. In some embodiments, thebottom, middle, and top layers 212-216 include different materials.

In some embodiments of dispensing a liquid material of top layer 216,referring now to FIG. 5C, the image sensor 52 captures an image 216 c ofthe top layer 216 during the dispensing. Specifically, the capturedimage 216 c shows a rippled and corrugated top layer 216 because thedispensed material of top layer 216 is liquid. For example, the capturedimage 216 c of the top layer 216 has a pitch P3 and/or an arc feature A3at the position S3 over the first wafer W1. The image processor 53 shownin FIG. 4A receives the captured image 216 c during the coating process(i.e., during dispensing material of the top layer 216). Then, the imageprocessor 53 compares the captured image 216 c of the top layer 216 to acorresponding reference image 540 (e.g., a reference image 216 r of adesirable top layer as shown in FIG. 6C), and then sends the comparisonresult to the controller 60 for the processing of the next wafer, suchas a second wafer W2 which will be discussed in greater detail belowwith respect to FIGS. 7A-8E.

Returning to FIG. 1A, the method M then proceeds to block S109 where thefirst top layer is pre-baked. With reference to FIG. 2G, in someembodiments of block S109, the pre-baking process 220 may be performedat an elevated temperature to evaporate the solvent in the top layer 216for a time duration sufficient to cure and dry the top layer 216. It isnoted that the number of layers in the tri-layer resist 210 isexemplary.

Returning to FIG. 1A, the method M then proceeds to block S110 where thefirst top layer is exposed to radiation. With reference to FIG. 2H, insome embodiments of block S110, the tri-layer resist 210 is exposed toradiation 222 in a lithography system. In some embodiments, theradiation 222 may be an I-line (365 nm), a DUV radiation such as KrFexcimer laser (248 nm) or ArF excimer laser (193 nm), a EUV radiation(e.g., 13.8 nm), an e-beam, an x-ray, an ion beam, or other suitableradiations. The exposure may be performed in air, in a liquid (immersionlithography), or in a vacuum (e.g., for EUV lithography and e-beamlithography). In some embodiments, the radiation 222 is patterned with aphotomask or reticle (not shown), such as a transmissive mask or areflective mask, which may include resolution enhancement techniquessuch as phase-shifting and/or optical proximity correction (OPC). Insome other embodiments, the radiation 222 is directly modulated with apredefined pattern, such as an IC layout, without using a photomask(maskless lithography).

In some embodiments, the radiation 222 irradiates portions 210A of thetri-layer resist 210 according to a pattern 208, either with a mask ormaskless. Specifically, the irradiated portions 210A of the tri-layerresist 210 include portions of the bottom, middle, and top layers 212,214, and 216 exposed by the pattern 208. In some embodiments, thetri-layer resist 210 is a positive resist and the irradiated portions210A become soluble in a developer. In alternative embodiments, thetri-layer resist 210 is a negative resist and the unexposed portions210B become insoluble in a developer.

Returning to FIG. 1A, the method M then proceeds to block S111 where thefirst top layer is post-baked. With reference to FIG. 2I, in someembodiments of block S111, a post-baking process 224 is performed on theradiation-sensitive material 204. In some embodiments, the post-bakeprocess 224 may be used in order to assist in the generating,dispersing, and reacting of the acid/base/free radical generated fromthe impingement of the energy upon the photoactive compounds in thetri-layer resist 210 during the exposure in the radiation 222. Suchassistance helps to create or enhance chemical reactions which generatechemical differences and different polarities between the irradiatedportions 210A and the unexposed portions 210B within the tri-layerresist 210. These chemical differences results in differences in thesolubility between the irradiated portions 210A and the unexposedportions 210B.

Returning to FIG. 1A, the method M then proceeds to block S112 where thefirst top layer is patterned using a first developer applied by a secondnozzle at a fourth distance from the first target layer, and an image ofthe first developer is captured during the applying. With reference toFIGS. 2J and 3D, in some embodiments of block S112, a developer 226 isapplied to the irradiated portions 210A of the tri-layer resist 210 onthe first wafer W1 by a dispensing nozzle 731 shown in FIG. 3D. Theirradiated portions 210A shown in FIG. 2I is removed by the developer226 and results in a patterned resist 210B. Specifically, the patternedresist 210B of the tri-layer resist 210 includes portions of the bottom,middle, and top layers 212, 214, and 216 underlying the pattern 208 (SeeFIG. 2H). In FIG. 3D, the dispensing nozzle 331 is separated from thetarget layer 204 by a distance D4.

In some embodiments, the dispensing nozzle 731 shown in FIG. 3D movesback and forth along a path during dispensing the developer 226. Forexample, the dispensing nozzle 731 can be moved by the second drivemechanism 82 in a predetermined path during dispensing the developer226. Therefore, the developer 226 can be more uniformly spread upon thefirst wafer W1. The path can be linear, spiral, or any other propershape to uniformly dispense the developer 226 onto the first wafer W1.In various embodiments of the present disclosure, the path is a linearpath corresponds to a radius of the first wafer W1.

In some embodiments, the developer 226 includes a developing chemicaldissolved in a solvent. In one example, the developer 226 is a positivetone developer, e.g., containing tetramethylammonium hydroxide (TMAH)dissolved in an aqueous solution. In another example, the developer 226is a negative tone developer, e.g., containing n-Butyl Acetate (nBA)dissolved in an organic solvent.

In detail, referring now to FIGS. 3D and 4C. FIG. 3D is a waferprocessing system 7 for developing the first wafer W1 in accordance withsome embodiments of the present disclosure. FIG. 7 is a block diagram ofthe wafer processing system 7 in accordance with some embodiments of thepresent disclosure. As shown in FIG. 3D, the wafer processing system 7further includes a processing chamber 70, a liquid dispensing module 80,an in-line monitoring module 90 (shown in FIG. 4C and also referred toas in-sequence monitoring module or a color imaging system), and acontroller 160 (shown in FIG. 4C).

As shown in FIG. 3D, the processing chamber 70 has an interior space 700defined by a number of walls, such as a lateral wall 701, a bottom wall702, and a top wall 703. The lateral wall 701 is connected to edges ofthe bottom wall 702 and extends away from the bottom wall 702. The topwall 703 is connected to the distal end of the lateral wall 701. In someembodiments, the interior space 700 is secluded from the ambientenvironment. The interior space 700 communicates to the ambientenvironment via a slot 705 formed on the lateral wall 701. The slot 705allows the transferring module to pass through.

In some embodiments, the processing chamber 70 includes a spin chuck 710(also referred to as a wafer stage in some embodiments) and a bowl(catch cup) 720. The spin chuck 710 and the bowl 720 are positioned inthe interior space 700. The spin chuck 710 is configured to holding androtating the first wafer W1. The first wafer W1 is placed on the spinchuck 710 and held in place by vacuum. The spin chuck 710 is rotatableand can be also referred to by a variety of names such as vacuum chuck.The spin chuck 710, for example, has a radius less than a radius of thefirst wafer W1. The first wafer W1 is positioned on the spin chuck 710such that the first wafer W1 is resting in a horizontal plane with theinactive surface, designated as the bottom, in contact with the spinchuck 710 and the opposite top surface is dispensed with desiredsolutions such as the developer 226 shown in FIG. 2J. The spin chuck 710is, for example, powered and rotated by a motor. The spin chuck 710holds the first wafer W1 by vacuum to allow spinning of first wafer W1.

In some embodiments, the first wafer W1 is enclosed by the bowl 720. Thebowl 720 can be moved up or down to surround the first wafer W1 andcollect drain and exhaust generated during developing processes. Forexample, drain and exhaust pipes can be connected to the underside ofthe bowl 720 to collect and drain out excess the developer 226 infollowing operations.

In FIG. 3D, the liquid dispensing module 80 includes one or more drivingelement 85 (shown in FIG. 4C), a first drive mechanism 81, a seconddrive mechanism 82, a dispensing nozzle 731, and a distance sensor 55,in accordance with some embodiments. The driving element 85 shown inFIG. 4C, such as a motor, is controlled by the controller 160 and iscoupled to the first drive mechanism 81 and the second drive mechanism82. The driving element 85 shown in FIG. 4C is used to actuate the firstdrive mechanism 81 to move in the vertical direction Y (as shown in FIG.3E). In some embodiments, the first drive mechanism 81 is rotatableabout a vertical axis as well. In some embodiments, the driving element45 is a programmable controller or the like.

In some embodiments, the dispensing nozzle 731 is mounted at the seconddrive mechanism 82. The dispensing nozzle 731 is used to apply chemicalsolutions to the first wafer W1. The dispensing nozzle 731 is connectedto a liquid source (not shown in figures) to receive the chemicalsolutions.

In some embodiments, the liquid dispensing module 80 controls dispensingdesired solutions such as the developer 226. For example, the dispensingnozzle 731 controls to dispense the developer 226 onto the first waferW1, and the second drive mechanism 82 (see FIG. 4C) controls movementsof the dispensing nozzles 731 while dispensing the developer 226. Insome embodiments, the dispensing nozzle 731 can be configured to drop aspecific quantity of developer 226 onto the first wafer W1 in the formof a puddle or to spray the desired quantity of developer 226 onto thefirst wafer W1 in the form of a mist.

In some embodiments, in some spin developing processes, the solution isdispensed prior to rotating the wafer, which is referred to as staticdispense. However, in the methods according to various embodiments ofthe present disclosure, the developer 226 is dispensed on the spinningfirst wafer W1, which is referred to as dynamic dispense. Referring toFIG. 3D, the first wafer W1 is rotated at a first rotating speed, andthen the developer 226 is dispensed onto the first wafer W1 at the firstrotating speed. For example, the first wafer W1 can be controlled by thespin chuck 710, and reach the first rotating speed. After the operationof dispensing the developer 226 onto the first wafer W1, the first waferW1 is rotated at a second rotating speed to spread the developer 226onto the first wafer W1 uniformly.

In FIG. 4C, the in-line monitoring module 90 includes an image sensor92, an image processor 93, and a reference image database 94, inaccordance with some embodiments. The image sensor 92 (see FIG. 3D) islocated at the interior space 700 of the processing chamber 70. In someembodiments, the image sensor 92 has a field of view (FOV) covering thespin chuck 710, so that the image sensor 92 can capture an image of awafer held by the spin chuck 710. In some embodiments, the image sensor92 is mounted at the bowl 720. In some embodiments, the image sensor 92includes a charge-coupled device (CCD).

In FIGS. 3D and 4C, the image processor 93 is connected to the imagesensor 92 to receive the captured image from the image sensor 92 duringthe developing process. Then, the image processor 93 compares the imagecaptured by the image sensor 92 to a reference image 940 stored in areference image database 94 and thus produce a comparison result showingthe differences between the two. The comparison result can be used todetermine a height of the dispensing nozzle 731 for processing of thenext wafer, such as a second wafer W2 which will be discussed in greaterdetail below with respect to FIGS. 7A-8E. The second wafer W2 may beprocessed in the processing chamber 70 after the processing of the firstwafer W1.

In some embodiments, the controller 160 send a control signal to thedriving element 85 of the liquid dispensing module 80 to actuate thefirst drive mechanism 81 moving in the vertical direction Y (as shown inFIG. 3E). Accordingly, the dispensing nozzle 731 mounted at the seconddrive mechanism 82 are able to move relatively to the first wafer W1 inthe vertical direction Y. In some embodiments, the controller 160 caninclude a central processing unit (CPU), a memory, and support circuits,e.g., input/output circuitry, power supplies, clock circuits, cache, andthe like. The memory is connected to the CPU. In addition, althoughillustrated as a single computer, the controller 160 can be adistributed system, e.g., including multiple independently operatingprocessors and memories.

In some embodiments of dispensing a developer 226, referring now to FIG.5D, the image sensor 92 captures an image 226 c of the developer 226during the dispensing. Specifically, the captured image 226 c shows arippled and corrugated developer 226 because the dispensed developer 226is liquid. For example, the captured image 226 c has a pitch P4 and/oran arc feature A4 at a position S4 over the first wafer W1. The imageprocessor 93 shown in FIG. 4C receives the captured image 226 c from theimage sensor 92 during the developing process (i.e., during dispensingthe developer 226). Then, the image processor 93 compares the capturedimage 226 c of the developer 226 to a corresponding reference image 940(e.g., a reference image 226 r of a desirable developer as shown in FIG.6D), and then sends the comparison result to the controller 160 for theprocessing of the next wafer, such as a second wafer W2 which will bediscussed in greater detail below with respect to FIGS. 7A-8E.

Returning to FIG. 1B, the method M then proceeds to block S113 where thesecond nozzle is vertically moved. With reference to FIG. 3E, in someembodiments of block S113, the first drive mechanism 81 may lower thedispensing nozzle 731 to a predetermined height, such that thedispensing nozzle 731 will be separated from the target layer 204 by adistance D5 which is different from the distance D4 shown in FIG. 3D.The difference between distances D4 and D5 is associated with adifference between the viscosities of the developer 226 and a rinsesolution 228 which will be subsequently dispensed on the developedtri-layer resist 210. In some embodiment, the viscosity of the rinsesolution 228 may be lower than that of the bottom layer 212.

Details of vertically moving the dispensing nozzle 731 can be referrednow to FIGS. 3E and 4D. FIG. 3E is a wafer processing system 7 inaccordance with some embodiments of the present disclosure. FIG. 4D is ablock diagram of the wafer processing system 7 in accordance with someembodiments of the present disclosure.

As shown in FIG. 3E, the distance sensor 95 is mounted at a distal endof the second drive mechanism 82 to detect a distance between thedispensing nozzle 731 and the first wafer W1. The distance sensor 95 maybe a real time monitor and feedback a height of the dispensing nozzle731. The controller 60 (see FIG. 4D) is connected to the distance sensor95 to periodically retrieve the electronic signal from the distancesensor 95.

The driving element 85, such as a motor, is controlled by the controller160 and is coupled to the first drive mechanism 81. Specifically, thecontroller 160 is configured to send a control signal to the drivingelement 85 of the liquid dispensing module 80 to actuate the first drivemechanism 81 moving in the vertical direction Y (as shown in FIG. 3E).In some embodiments, the control signal from the controller 160 isassociated with a measured distance from the distance sensor 55. Forexample, if the measured distance is less than the predetermineddistance D5 which is associated with dispensing a rinse solution, thecontroller 160 can provide a control signal to trigger the drivingelement 85 to vertically move the dispensing nozzle 731.

When the distance between the dispensing nozzle 731 and the target layer204 is substantially equal to the distance D5, the controller 160 willsend a control signal to the driving element 85 to stop (or halt) theoperation of the driving element 85. Accordingly, the dispensing nozzle731 and the target layer 204 will maintain the distance D5 therebetweenin the vertical direction Y.

Returning to FIG. 1B, the method M then proceeds to block S114 where thefirst top layer is rinsed using a first rinse solution applied by thesecond nozzle at a fifth distance from the first target layer, and animage of the first rinse solution is captured during the rinsing. Withreference to FIG. 2K and FIG. 3E, in some embodiments of block S114, arinse solution 228 is dispensed onto the first wafer W1 by thedispensing nozzle 731 above the first wafer W1 and separated from thetarget layer 204 by a distance D5. The rinse solution 228 can bedispensed above the center of the first wafer W1, or dispensed alongwith a predetermined path. The predetermined path can be linear, spiral,or any other proper shape to uniformly dispense the rinse solution 228onto the first wafer W1. In some embodiments, the rinse solution 228 isdispensed back and forth along the linear path corresponds to a radiusof the first wafer W1. In some embodiments, the rinse solution 228 canbe any proper solvent to effectively wash away the irradiated portions210A of the tri-layer resist 210, which is reacted with the developer226 shown in FIG. 2J. In various embodiments of the present disclosure,the rinse solution 228 is deionized water.

In detail, referring now to FIGS. 3E and 4C. In FIG. 4C, in someembodiments, the liquid dispensing module 80 controls dispensing desiredsolutions such as the rinse solution 228. For example, the dispensingnozzle 731 is controlled by the liquid dispensing module 80 to dispensethe rinse solution 228 onto the first wafer W1. The second drivemechanism 82 (see FIG. 4C) controls movements of the dispensing nozzles731 while dispensing the rinse solution 228. In some embodiments, thedispensing nozzle 731 can either be configured to drop a specificquantity onto the first wafer W1 in the form of a puddle or to spray thedesired quantity onto the first wafer W1 in the form of a mist. In othervarious embodiments of the present disclosure, the liquid dispensingmodule 80 further includes another nozzle (not shown). In FIG. 3E,dispensing of the rinse solution 228 can be integrated into one nozzleto perform the developing and rinsing processes. In some embodiments,drain and exhaust pipes can be connected to the underside of the bowl720 to collect and drain out a rinse solution 228.

In some embodiments of dispensing the rinse solution 228, referring nowto FIG. 5E, the image sensor 92 captures an image 228 c of the rinsesolution 228 during the dispensing. Specifically, the captured image 228c is a rippled and corrugated rinse solution 228 because the rinsesolution 228 is liquid. For example, the captured image 228 c has apitch P5 and/or an arc feature A5 at a position S5 over the first waferW1. The image processor 93 shown in FIG. 4C receives the captured image228 c from the image sensor 92 during the rinsing process (i.e., duringdispensing the rinse solution 228). Then, the image processor 93compares the captured image 228 c to a corresponding reference image 940(e.g., a reference image 228 r of a desirable rinse solution as shown inFIG. 6B), and then sends the comparison result to the controller 160 forthe processing of the next wafer, such as a second wafer W2 which willbe discussed in greater detail below with respect to FIGS. 7A-8E.

Returning to FIG. 1B, the method M then proceeds to block S115 where thefirst target layer patterned using the first multi-layer resist as amask. With reference to FIG. 2L, in some embodiments of block S115, thetarget layer 204 is patterned using the patterned resist 210B as an etchmask, thereby transferring the pattern of the patterned resist 210B tothe target layer 204. For example, the target layer 204 may be etchedusing a dry (plasma) etching, a wet etching, and/or other etchingmethods. In some embodiments, the patterned resist 210B may be partiallyor completely consumed during the etching of the target layer 204. Insome embodiments, any remaining portion of the patterned resist 210B maybe stripped off, leaving the target layer 204 over the first wafer W1.The method M may proceed to forming a final pattern or an IC device onthe target layer 204.

Referring now back to FIG. 1B and FIG. 1C, the method M then proceeds toblock S116 where a second target layer is formed over a second wafer.Referring to FIG. 7A, in some embodiments of block S116, the secondwafer W2 includes one or more layers of material or composition. In someembodiments, the second wafer W2 is a semiconductor substrate asdiscussed previously with respect to the first wafer W1. As shown inFIG. 7A, a target layer 904 is formed on the second wafer W2. In someembodiments, the target layer 904 is a hard mask layer includingmaterial(s) such as amorphous silicon (a-Si), silicon oxide, siliconnitride (SiN), titanium nitride, or other suitable material orcomposition. In some embodiments, the target layer 204 includes ananti-reflection coating (ARC) layer such as a nitrogen-freeanti-reflection coating (NFARC) layer including material(s) such assilicon oxide, silicon oxygen carbide, or plasma enhanced chemical vapordeposited silicon oxide.

Returning to FIG. 1B, the method M then proceeds to block S117 where thefirst nozzle is vertically moved in response to a comparison resultbetween the captured image of the first bottom layer with a referenceimage of a bottom layer. In some embodiments of block S117, the imageprocessor 53 (See FIG. 4A) compares the captured image 212 c (See FIG.5A) of the bottom layer 212 to the reference image 212 r (See FIG. 6A)of a desirable bottom layer and generates a comparison result. The imageprocessor 53 then sends the comparison result to the controller 60 (SeeFIG. 4A). Thereafter, the controller 60 can control the driving element45 to trigger or actuate vertical movement of the first drive mechanism41 in response to the comparison result, thus resulting in verticalmovement of the dispensing nozzle 331 (See FIG. 8A), such that thedispensing nozzle 331 can be at a distance D6 from the target layer 904.In this way, the dispensing nozzle 331 can be lifted or lower inresponse to the comparison result.

In some embodiments, the reference image 212 r of the desirable bottomlayer shown in FIG. 6A shows a rippled and corrugated bottom layerhaving a pitch P6 at the position S1 and having an arc feature A6 at theposition S1. In some embodiments, the pitch P1 of the captured image 212c of the bottom layer 212 is different from the pitch P6 of thereference image 212 r of the desirable bottom layer. In some otherembodiments, the arc feature A1 of the captured image 212 c of thebottom layer 212 is different form the arc feature A6 of the referenceimage 212 r of the desirable bottom layer.

The image processor 53 can generate a comparison result based on thedifference between the captured image 212 c and the reference image 212r. The dispensing nozzle 331 can be lifted or lowered in response to thecomparison result, such that the dispensing nozzle 331 will be separatedfrom the target layer 904 by a distance D6 that is different from thedistance D1 as discussed previously with respect to FIG. 3A. In someembodiments, the distance D6 is greater than the distance D1; in otherembodiments, the distance D6 is less than the distance D1. This can bedue, at least in part, to the different chemical viscosities being used,and can be determined based on real-time feedback of measurement, priortest results or by mathematical process. In this manner, the bottomlayer of the later-processed wafer W2 will have better thicknessuniformity (i.e., better surface flatness) than that of thepreviously-processed wafer W1.

Returning to FIG. 1B, the method M then proceeds to block S118 where thesecond target layer is coated with a second bottom layer of a secondmulti-layer resist using the first nozzle at a sixth distance from thesecond target layer.

With reference to FIGS. 7B and 8A, in some embodiments of block S118,the bottom layer 912 is coated on the target layer 904. In detail, afirst liquid film, such as a liquid material of the bottom layer 912, isdispensed on the second wafer W2 through the dispensing nozzle 331separated from the target layer 904 by the distance D6. The bottom layer912 includes a material substantially the same as that of the bottomlayer 212 shown in FIG. 2B, and detailed material examples of the bottomlayer 912 is thus not repeated for the sake of brevity. Because thedistance D6 is optimized using the comparison result between a capturedbottom layer image of the previously-processed wafer W1 and a referencebottom layer image, the bottom layer 912 can have an improved thicknessuniformity compared to the bottom layer 212 coated on thepreviously-processed wafer W1.

Returning to FIG. 1B, the method M then proceeds to block S119 where thesecond bottom layer is pre-baked. With reference to FIG. 7C, in someembodiments of block S119, a pre-baking process 920 may be performed atan elevated temperature to evaporate the solvent for the bottom layer912 for a time duration sufficient to cure and dry the bottom layer 912.

Returning to FIG. 1B, the method M then proceeds to block S120 where thefirst nozzle is vertically moved in response to a comparison resultbetween the captured image of the first middle layer and a referenceimage of a middle layer. In some embodiments of block S120, the imageprocessor 53 (See FIG. 4A) compares the captured image 214 c (See FIG.5B) of the middle layer 214 with the reference image 214 r (See FIG. 6B)of a desirable middle layer and generates a comparison result. The imageprocessor 53 then sends the comparison result to the controller 60 (SeeFIG. 4A). Thereafter, the controller 60 can control the driving element45 to trigger or actuate vertical movement of the first drive mechanism41 in response to the comparison result, thus resulting in verticalmovement of the dispensing nozzle 331, such that the dispensing nozzle331 can be at a distance D7 from the target layer 904. In this way, thedispensing nozzle 331 can be lifted or lower in response to thecomparison result.

In some embodiments, the reference image 214 r of the desirable middlelayer shown in FIG. 6B shows a rippled and corrugated middle layerhaving a pitch P7 at the position S2 and having an arc feature A7 at theportion S2. In some embodiments, the pitch P2 of the captured image 214c of the middle layer 214 is different from the pitch P7 of thereference image 214 r of the desirable middle layer. In some otherembodiments, the arc feature A2 of the captured image 214 c of themiddle layer 214 is different form the arc feature A7 of the referenceimage 214 r of the desirable middle layer.

The image processor 53 can generate a comparison result based on thedifference between the captured image 214 c and the reference image 214r. The dispensing nozzle 331 can be lifted or lowered in response to thecomparison result, such that the dispensing nozzle 331 will be separatedfrom the target layer 904 by a distance D7 that is different from thedistance D2 as discussed previously with respect to FIG. 3B. In someembodiments, the distance D7 is greater than the distance D2, in otherembodiments, the distance D7 is less than the distance D2. This can bedue, at least in part, to the different chemical viscosities being used,and can be determined based on real-time feedback of measurement, priortest results or by mathematical process. In this manner, the middlelayer of the later-processed wafer W2 will have better thicknessuniformity (i.e., better surface flatness) than that of thepreviously-processed wafer W1.

Returning to FIG. 1B, the method M then proceeds to block S121 where thesecond bottom layer is coated with a second middle layer of the secondmulti-layer resist using the first nozzle at a seventh distance from thesecond target layer.

With reference to FIGS. 7D and 8B, in some embodiments of block S121,the middle layer 914 is coated on the bottom layer 912. In detail, asecond liquid film, such as a liquid material of the middle layer 914,is dispensed on the second wafer W2 through the dispensing nozzle 331separated from the target layer 904 by the distance D7. The middle layer914 includes a material substantially the same as that of the middlelayer 214 shown in FIG. 2D, and detailed material examples of the middlelayer 914 is thus not repeated for the sake of brevity. Because thedistance D7 is optimized using the comparison result between a capturedmiddle layer image of the previously-processed wafer W1 and a referencemiddle layer image, the middle layer 914 can have an improved thicknessuniformity compared to the middle layer 214 coated on thepreviously-processed wafer W1.

Returning to FIG. 1B, the method M then proceeds to block S122 where thesecond middle layer is pre-baked. With reference to FIG. 7E, in someembodiments of block S122, the pre-baking process 920 may be performedat an elevated temperature to evaporate the solvent in the middle layer914 a time duration sufficient to cure and dry the middle layer 914.

Returning to FIG. 1B, the method M then proceeds to block S123 where thefirst nozzle is vertically moved in response to a comparison resultbetween the captured image of the first top layer and a reference imageof a top layer. In some embodiments of block S123, the image processor53 (See FIG. 4A) compares the captured image 216 c (See FIG. 5C) of thetop layer 216 with the reference image 216 r (See FIG. 6C) of adesirable top layer and generates a comparison result. The imageprocessor 53 then sends the comparison result to the controller 60 (SeeFIG. 4A). Thereafter, the controller 60 can control the driving element45 to trigger or actuate vertical movement of the first drive mechanism41 in response to the comparison result, thus resulting in verticalmovement of the dispensing nozzle 331, such that the dispensing nozzle331 is at a distance D8 from the target layer 904. In this way, thedispensing nozzle 331 can be lifted or lower in response to thecomparison result.

For example, the reference image 216 r of the desirable top layer shownin FIG. 6C shows a rippled and corrugated top layer having a pitch P8 atthe position S3 and having an arc feature A8 at the portion S3. In someembodiments, the pitch P3 of the captured image 216 c of the top layer216 is different from the pitch P8 of the reference image 216 r of thedesirable top layer. In some embodiments, the arc feature A3 of thecaptured image 216 c of the top layer 216 is different form the arcfeature A8 of the reference image 216 r of the desirable top layer.

The image processor 53 can generate a comparison result based on thedifference between the captured image 216 c and the reference image 216r. The dispensing nozzle 331 can be lifted or lowered in response to thecomparison result, such that the dispensing nozzle 331 will be separatedfrom the target layer 904 by a distance D8 that is different from thedistance D3 as discussed previously with respect to FIG. 3C. In someembodiments, the distance D8 is greater than the distance D3; in otherembodiments, the distance D8 is less than the distance D3. This can bedue, at least in part, to the different chemical viscosities being used,and can be determined based on real-time feedback of measurement, priortest results or by mathematical process. In this manner, the top layerof the later-processed wafer W2 will have better thickness uniformity(i.e., better surface flatness) than that of the previously-processedwafer W1.

Returning to FIG. 1C, the method M then proceeds to block S124 where thesecond middle layer is coated with a second top layer of the secondmulti-layer resist using the first nozzle at an eighth distance from thefirst target layer.

With reference to FIGS. 7F and 8C, in some embodiments of block S124,the top layer 916 is coated on the middle layer 914. In detail, a thirdliquid film, such as a liquid material of the top layer 916, isdispensed on the second wafer W2 through the dispensing nozzle 331separated from the target layer 904 by the distance D8. The top layer916 includes a material substantially the same as that of the top layer216 shown in FIG. 2F, and detailed material examples of the top layer916 is thus not repeated for the sake of brevity. Because the distanceD8 is optimized using the comparison result between a captured top layerimage of the previously-processed wafer W1 and a reference top layerimage, the top layer 916 can have an improved thickness uniformitycompared to the top layer 216 coated on the previously-processed waferW1.

Returning to FIG. 1C, the method M then proceeds to block S125 where thesecond top layer is pre-baked. With reference to FIG. 7G, in someembodiments of block S125, the pre-baking process 920 may be performedat an elevated temperature to evaporate the solvent in the top layer 916for a time duration sufficient to cure and dry the top layer 916. Insome other embodiments, the tri-layer resist 910 may be replaced by abi-layered structure or a multilayered structure.

Returning to FIG. 1C, the method M then proceeds to block S126 where thesecond top layer is exposed to radiation. With reference to FIG. 7H, insome embodiments of block S126, the tri-layer resist 910 is exposed toradiation 922 in a lithography system. Detailed description about theexposure is discussed previously with respect to block S110, and is thusnot repeated for the sake of brevity.

In some embodiments, the radiation 922 irradiates portions 910A of thetri-layer resist 910 according to a pattern 908, either with a mask ormaskless. Specifically, the irradiated portions 910A of the tri-layerresist 910 include portions of the bottom, middle, and top layers 912,914, and 916 exposed by the pattern 908. In some embodiments, thetri-layer resist 910 is a positive resist and the irradiated portions910A become soluble in a developer. In alternative embodiments, thetri-layer resist 910 is a negative resist and the unexposed portions910B become insoluble in a developer.

Returning to FIG. 1C, the method M then proceeds to block S127 where thesecond top layer is post-baked. With reference to FIG. 7I, in someembodiments of block S127, a post-baking process 924 is performed on theradiation-sensitive material 204. In some embodiments, the post-bakeprocess 924 may be used in order to assist in the generating,dispersing, and reacting of the acid/base/free radical generated fromthe impingement of the energy upon the photoactive compounds in thetri-layer resist 910 during the exposure in the radiation 922. Suchassistance helps to create or enhance chemical reactions which generatechemical differences and different polarities between the irradiatedportions 910A and the unexposed portions 910B within the tri-layerresist 910. These chemical differences also cause differences in thesolubility between the irradiated portions 910A and the unexposedportions 910B.

Returning to FIG. 1C, the method M then proceeds to block S128 where thesecond nozzle is vertically moved in response to a comparison resultbetween the captured image of the first developer and a reference imageof a developer. In some embodiments of block S128, the image processor93 (See FIG. 4C) compares the captured image 226 c (See FIG. 5D) of thedeveloper 226 to the reference image 226 r (See FIG. 6D) of a desirabledeveloper and generates a comparison result. The image processor 93 thensends the comparison result to the controller 160 (See FIG. 4C).Thereafter, the controller 160 can control the driving element 85 totrigger or actuate vertical movement of the first drive mechanism 81 inresponse to the comparison result, thus resulting in vertical movementof the dispensing nozzle 731 (See FIG. 8D). In this way, the dispensingnozzle 731 can be lifted or lower in response to the comparison result.

In some embodiments, the reference image 226 r of the desirabledeveloper shown in FIG. 6D is a rippled and corrugated developer havinga pitch P9 at the position S4 and having an arc feature A9 at theportion S4. In some embodiments, the pitch P4 of the captured image 226c of the developer 226 is different from the pitch P9 of the referenceimage 226 r of the desirable developer. In some embodiments, the arcfeature A4 of the captured image 226 c of the developer 226 is differentform the arc feature A9 of the reference image 214 r of the desirabledeveloper.

The image processor 93 can generate a comparison result based on thedifference between the captured image 226 c and the reference image 226r. The dispensing nozzle 731 can be lifted or lowered in response to thecomparison result, such that the dispensing nozzle 731 will be separatedfrom the target layer 904 by a distance D9 that is different from thedistance D4 as discussed previously with respect to FIG. 3D. In someembodiments, the distance D9 is greater than the distance D4; in otherembodiments, the distance D9 is less than the distance D4. This can bedue, at least in part, to the different chemical viscosities being used,and can be determined based on real-time feedback of measurement, priortest results or by mathematical process. In this manner, the patternedresist 910B of the later-processed wafer W2 will have better criticaldimension (CD) uniformity (i.e., CDs in a center region of a wafer maybe substantially the same as the CDs in a peripheral region of thewafer) than that of the previously-processed wafer W1.

Returning to FIG. 1C, the method M then proceeds to block S129 where thesecond top layer is patterned using a second developer applied by thesecond nozzle at a ninth distance from the second target layer. Withreference to FIG. 7J, in some embodiments of block S118, the developer926 is dispensing on the tri-layer resist 210 through the dispensingnozzle 731 separated from the target layer 904 by the distance D9. Thedeveloper 926 includes a material substantially the same as that of thedeveloper 226 shown in FIG. 2J, and detailed material examples of thedeveloper 926 is thus not repeated for the sake of brevity. Because thedistance D9 is optimized using the comparison result between a captureddeveloper image of the previously-processed wafer W1 and a referencedeveloper image, the developer 926 can result in an improved CDuniformity in a patterned photoresist compared to the developer 226dispensed on the previously-processed wafer W1.

If the dispensing nozzle 731 is separated from the target layer 904 bythe distance D4 shown in FIG. 3D rather than the distance D9, thepatterned resist 910B may have a non-uniform CD (i.e., poor CD) on thesecond wafer W2. For example, CDs in a center region of a wafer may begreater than the CDs in a peripheral region of the wafer. However,because the developer 926 is dispensed using the dispensing nozzle 731at the distance D9 rather than the distance D4, CD uniformity of thepatterned resist 910B can be improved compared to the patterned resist210B of the previously-processed wafer W1.

Returning to FIG. 1C, the method M then proceeds to block S130 where thesecond nozzle is vertically moved in response to a comparison resultbetween the captured image of the first rinse solution and a referenceimage of a rinse solution. In some embodiments of block S130, the imageprocessor 93 (See FIG. 4C) compares the captured image 228 c (See FIG.5E) of the rinse solution 228 to the reference image 228 r (See FIG. 6E)of a desirable rinse solution and generates a comparison result. Theimage processor 93 then sends the comparison result to the controller160 (See FIG. 4A). Thereafter, the controller 160 can control thedriving element 85 to trigger or actuate vertical movement of the firstdrive mechanism 81 in response to the comparison result, thus resultingin vertical movement of the dispensing nozzle 731 (See FIG. 8E). In thisway, the dispensing nozzle 731 can be lifted or lower in response to thecomparison result.

In some embodiments, the reference image 228 r of the desirable rinsesolution shown in FIG. 6E is a rippled and corrugated rinse solutionhaving a pitch P10 at the position S5 and having an arc feature A10 atthe position S5. In some embodiments, the pitch P5 of the captured image228 c of the rinse solution 228 is difference from the pitch P10 of thereference image 228 r of the desirable rinse solution. In someembodiments, the arc feature A5 of the captured image 228 c of the rinsesolution 228 is different form the arc feature A10 of the referenceimage 228 r of the desirable rinse solution.

The image processor 93 can generate a comparison result based on thedifference between the captured image 228 c and the reference image 228r. The dispensing nozzle 731 can be lifted or lowered in response to thecomparison result, such that the dispensing nozzle 731 will be separatedfrom the target layer 904 by a distance D10 that is different from thedistance D5 as discussed previously with respect to FIG. 3E. In someembodiments, the distance D10 is larger than the distance D5; in otherembodiments, the distance D10 is less than the distance D5. This can bedue, at least in part, to the different chemical viscosities being used,and can be determined based on real-time feedback of measurement, priortest results or by mathematical process. In this manner, the patternedresist 910B of the later-processed wafer W2 will have better CDuniformity than that of the previously-processed wafer W1.

Returning to FIG. 1C, the method M then proceeds to block S131 where thesecond top layer is rinsed using a second rinse solution applied by thesecond nozzle at a tenth distance from the second target layer. Withreference to FIG. 7K, in some embodiments of block S131, the rinsesolution 928 is dispensing on the patterned resist 210B through thedispensing nozzle 731 separated from the target layer 904 by thedistance D10. The rinse solution 928 includes a material substantiallythe same as that of the rinse solution 228 shown in FIG. 2K, anddetailed material examples of the rinse solution 928 is thus notrepeated for the sake of brevity. Because the distance D10 is optimizedusing the comparison result between a captured rinse solution image ofthe previously-processed wafer W1 and a reference rinse solution image,the rinse solution 928 can result in an improved CD uniformity in therinsed photoresist compared to the rinse solution 228 dispensed on thepreviously-processed wafer W1.

If the dispensing nozzle 731 is separated from the target layer 904 bythe distance D5 shown in FIG. 3E rather than the distance D10, thepatterned resist 910B may have a non-uniform CD (i.e., poor CD) on thesecond wafer W2. For example, CDs in a center region of a wafer may begreater than the CDs in a peripheral region of the wafer. However,because the rinse solution 928 is dispensed using the dispensing nozzle731 at the distance D10 rather than the distance D5, CD uniformity ofthe patterned resist 910B can be improved.

Returning to FIG. 1C, the method M then proceeds to block S132 where thesecond target layer is patterned using the second multi-layer resist asa mask. With reference to FIG. 7L, in some embodiments of block S132,the target layer 904 is patterned using the patterned resist 910B as anetch mask, thereby transferring the pattern of the patterned resist 910Bto the target layer 904. For example, the target layer 904 may be etchedusing a dry (plasma) etching, a wet etching, and/or other etchingmethods. In some embodiments, the patterned resist 910B may be partiallyor completely consumed during the etching of the target layer 904. Insome embodiments, any remaining portion of the patterned resist 910B maybe stripped off, leaving the target layer 904 over the second wafer W2.The method M may proceed to forming a final pattern or an IC device onthe target layer 904. In a non-limiting example, the second wafer W2 isa semiconductor substrate and the method M proceeds to forming fin fieldeffect transistor (FinFET) structures.

Based on the above discussion, it can be seen that the presentdisclosure offers advantages. It is understood, however, that otherembodiments may offer additional advantages, and not all advantages arenecessarily disclosed herein, and that no particular advantages isrequired for all embodiments. One advantage is that thickness uniformity(i.e., flatness) of a multi-layer photoresist (e.g., a tri-layerphotoresist) can be improved, because different materials of themulti-layer photoresist having different viscosities are coated atdifferent nozzle heights. Another advantage is that a spin-on layer(e.g., bottom, middle or top layer of a tri-layer photoresist) on thelater-processed wafer can have better thickness uniformity than that ofthe previously-processed wafer, because the spin-on layer on thelater-processed wafer is coated at a fine-tuned nozzle height that isobtained by comparing a captured image of the spin-on layer on thepreviously-processed wafer to a reference image associated with adesirable spin-on layer. Another advantage is that the patternedphotoresist on the later-processed wafer can have better CD uniformitythan that of the previously-processed wafer, because the developer (orrinse solution) applied to the later-processed wafer is dispensed at afine-tuned nozzle height that is obtained by comparing a captured imageof the developer (or rinse solution) on the previously-processed waferto a reference image associated with a desirable developer (or rinsesolution).

In some embodiments, a photolithography method includes dispensing afirst liquid onto a first target layer formed over a first wafer througha nozzle at a first distance from the first target layer; capturing animage of the first liquid on the first target layer; patterning thefirst target layer after capturing the image of the first liquid;comparing the captured image of the first liquid to a first referenceimage to generate a first comparison result; responsive to the firstcomparison result, positioning the nozzle and a second wafer such thatthe nozzle is at a second distance from a second target layer on thesecond wafer; dispensing a second liquid onto the second target layerformed over the second wafer through the nozzle at the second distancefrom the second target layer; and patterning the second target layerafter dispensing the second liquid.

In some embodiments, a photolithography method includes dispensing afirst liquid toward a target layer through a nozzle at a first distancefrom the target layer; moving the nozzle such that the nozzle is at asecond distance from the target layer, wherein the second distance isdifferent from the first distance; dispensing a second liquid toward thetarget layer through the nozzle at the second distance from the targetlayer; and patterning the target layer after dispensing the first liquidand the second liquid.

In some embodiments, a photolithography system includes a wafer stage, adispensing nozzle, an image sensor, an image processor, and acontroller. The wafer stage is configured to hold a wafer. Thedispensing nozzle is above the wafer stage. The image sensor isconfigured to capture an image of the wafer. The image processor isconfigured to compare the captured image to a reference image. Thecontroller is configured to lift or lower the dispensing nozzle inresponse to a result of comparing the captured image to the referenceimage.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A photolithography system, comprising: a waferstage configured to hold a wafer in a chamber; a dispensing nozzle abovethe wafer stage; a driving unit configured to displace the dispensingnozzle, wherein the driving unit includes a distance sensor disposedadjacent to the dispensing nozzle, and wherein the distance sensor isconfigured to detect a distance between the dispensing nozzle and thewafer; an imaging module including an image sensor configured to capturean image of the wafer and an image processor configured to compare thecaptured image to a reference image; and a controller configured to movethe driving unit in response to a result of comparing the captured imageto the reference image.
 2. The photolithography system of claim 1,wherein the driving unit includes: a first driving mechanism configuredto vertically adjust a distance between the dispensing nozzle and thewafer; a second driving mechanism connected to the first drivingmechanism, wherein the second driving mechanism extends horizontallyover the wafer; and a driving element coupled to the first drivingmechanism and the second driving mechanism, wherein the driving elementis configured to receive a control signal from the controller andsubsequently actuate the first driving mechanism to move vertically. 3.The photolithography system of claim 1, wherein the controller isconfigured to move the driving unit in response to the distance detectedby the distance sensor.
 4. The photolithography system of claim 1,wherein the distance sensor is mounted on a distal end of the drivingunit and adjacent to the dispensing nozzle.
 5. The photolithographysystem of claim 1, wherein the image sensor is positioned such that afield of view of the image sensor covers the wafer stage.
 6. Thephotolithography system of claim 1, wherein the image sensor includes acharge-coupled device.
 7. A photolithography system, comprising: a waferstage enclosed in a chamber and configured to hold a wafer; a dispensingmodule, including: a dispensing nozzle extending over the wafer stageand a driving mechanism mounted on a bottom wall of the chamber andconnected to the dispensing nozzle, wherein the driving mechanism isconfigured to vertically move the dispensing nozzle with respect to thewafer; an imaging module configured to capture an image of the wafer andsubsequently produce a signal; a controller connected to the dispensingmodule and the imaging module, wherein the controller is configured tomove the dispensing module with respect to the wafer in response to thesignal produced by the imaging module; and a sensor connected to thecontroller and operable to detect a separation distance between thedispensing nozzle and the wafer, wherein the sensor is disposed on adistal end of the dispensing module.
 8. The photolithography system ofclaim 7, wherein the driving mechanism includes: a vertical elementmounted on the bottom wall of the chamber, a horizontal elementconnected to the vertical element and extending over the wafer stage,and a driving element connected to the controller and configured toactuate the vertical element, thereby moving the dispensing nozzlerelative to the wafer stage.
 9. The photolithography system of claim 8,wherein the vertical element is rotatable about a vertical axis.
 10. Thephotolithography system of claim 7, wherein the imaging module includes:a sensor configured to capture the image of the wafer, a processor incommunication with the sensor and the controller, and a databaseincluding a reference image, wherein the processor is configured tocompare the captured image with the reference image to produce thesignal.
 11. The photolithography system of claim 10, further comprisinga catch cup surrounding the wafer stage, wherein the sensor is mountedon the catch cup above the wafer stage, such that the sensor has a fieldof view that covers an entirety of the wafer stage.
 12. Aphotolithography system, comprising: a wafer stage disposed in a chamberand configured to hold a wafer; a dispensing unit, including: a verticalcomponent mounted on an interior wall of the chamber, a horizontalcomponent connected to the vertical component and extending over thewafer stage, a nozzle affixed on the horizontal component and configuredto dispense a coating liquid on the wafer, and a motor configured tomove the vertical component, thereby adjusting a position of the nozzlerelative to the wafer; a distance sensor mounted on the dispensing unit;an image sensor configured to capture an image of the wafer; an imageprocessor configured to compare the image captured by the image sensorwith a reference image to produce a comparison dataset; and a controllerin communication with the dispensing unit, the distance sensor, and theimage processor, such that the controller is configured to adjustmovement of the dispensing unit relative to the wafer stage according tothe comparison dataset.
 13. The photolithography system of claim 12,further comprising a catch cup partially enclosing the wafer stage,wherein the image sensor is mounted on an upper portion of the catchcup, such that a field of view of the image sensor includes an entiretop surface of the wafer.
 14. The photolithography system of claim 13,wherein the catch cup further includes an exhaust system configured toremove excess coating liquid from the chamber.
 15. The photolithographysystem of claim 12, wherein the vertical component of the dispensingunit is rotatable about a vertical axis.
 16. The photolithography systemof claim 12, wherein the distance sensor is mounted on a distal end ofthe horizontal component of the dispensing unit to detect a distancebetween the nozzle and the wafer.
 17. The photolithography system ofclaim 12, wherein the image sensor includes a charge-coupled device. 18.The photolithography system of claim 12, wherein the wafer stage isrotatable about a vertical axis.
 19. The photolithography system ofclaim 1, further comprising a catch cup surrounding the wafer stage,wherein the image sensor is mounted on the catch cup above the waferstage, such that the sensor has a field of view that covers an entiretyof the wafer stage.
 20. The photolithography system of claim 7, furthercomprising an edge bead rinse (EBR) nozzle operable to supply a liquidsolution over the wafer.